With the advent of large scale farming on tracts of land measured in thousands of acres instead of tens of acres, and the development of farm machinery of massive size to handle such acreage, problems arose which were either non-existant or much more simply overcome by the small farm farmer. For example, in making a single pass of a colorless pesticide spray or fertilizer spray, the small farm farmer usually had no difficulty in determining the dividing line between the sprayed portion and the unsprayed portion and could therefore direct his equipment without much difficulty. However, with large scale machinery where a single pass may be as much as from 50 to 75 feet in width, it becomes a very serious problem to determine where to make the next pass. Too much pesticide or fertilizer or too little of either can cause severe damage to a crop, particularly, if the area of either overlap or skipping is of an order of magnitude of ten feet over a distance of 1 or 2 miles. Too much pesticide, i.e., a double dose for such a width can kill from one to three acres of crop through overdose or permit the crop to fail in an equivalent area because of failure to apply any dose whatever.
Prior art methods for combating this problem have included a scribing device such as taught in the U.S. Pat. to Maddox, No. 1,643,625, the patent to Liston, 831,961 and the patent to MacNair, 832,989; a disk-type marker such as taught in U.S. Pat. No. 3,503,451 to Eastman, and a foam marking device such as taught by Cooke, et al in U.S. Pat. No. 3,481,545.
While the scribing devices might have been quite satisfactory for passes up to ten feet in width, beyond that width such marks were difficultly visible, if at all. Other devices encountered difficulty because of the means of mounting devices, and if the apparatus was inadvertently backed up, very often the mount or the support arms were bent or broken.
The present invention contemplates a ground marker which in and of itself is not new (see U.S. Pat. Nos. 2,580,958 and 3,503,451) in combination, however, with a mounting means which enables greater flexibility and accomodation of the apparatus to changes in contour, and preferred embodiments of which also accommodate inadvertent backing up of the truck or apparatus with the distributing arms extended without damage.